@misc{04098d17-4116-4c31-b9f7-8c03b8c288b2,
abstract = {Solar energy is a renewable energy source which in the long term is important to develop<br/><br>
because the usage does not effect the environment in a negative way.<br/><br>
Increased energy exchange and cheaper production costs for solar collectors and solar cells<br/><br>
are main factors in making the solar energy commercially successful in the future.<br/><br>
Small scale solar collector systems are most common today because the heat storage time is<br/><br>
very limited. The heat is mostly stored in short time storage in an accumulator tank.<br/><br>
Large scale solar collector systems usually deliver the heat directly to the district heating net,<br/><br>
but there are also attempts to store solar heat in season storage.<br/><br>
The project EEBIS, energy efficiency constructed in society, is run by Lund Institute of<br/><br>
Technology and some construction and installation companies.<br/><br>
The result of this project is the building “Solgården” in Älvkarleby Sweden, a house<br/><br>
constructed to use the sun heat in the best possible way. One part of this project is the “solar<br/><br>
window” and the intention is to install 18 m2 solar windows at Solgården. To be able to<br/><br>
evaluate the performance of the solar window a solar window prototype was constructed.<br/><br>
The main purpose of this diploma work is to evaluate the heat insulating abilities but also to<br/><br>
evaluate the solar energy exchange of the solar window prototype.<br/><br>
The solar window is a new way of integrating solar energy in buildings combining solar<br/><br>
collectors, solar cells and sun shield in a window. The solar window has got movable<br/><br>
reflectors and solid solar hybrids mounted inside a double glass.<br/><br>
The reflectors concentrate the sunlight on the solar hybrids to make the expensive solar<br/><br>
collectors and solar cell areas smaller.<br/><br>
The reflectors are supposed to be closed on hot days (sun radiation &gt; 300 W/m2) to reflect the<br/><br>
sunlight on the solar hybrids and then generate electricity and heat and at the same time work<br/><br>
as a sun shield to the large solar window area. On cold days (sun radiation &lt; 50 W/m2) the<br/><br>
closed reflectors are used as an insulating wall. That is why the solar window construction has<br/><br>
to be well insulated, to avoid the heat in the house getting lost through the solar window.<br/><br>
In other cases the solar windows are supposed to be open to give passive sun heat to the<br/><br>
house. When the heat exchange, from the solar collectors, is low it can be complemented with<br/><br>
a pellet pan.<br/><br>
The construction is unique because it functions as a solar hybrid and a sun shield at the same<br/><br>
time it is installed in a window. This is based on the glass quality.<br/><br>
The glass, which is the most important component in a solar collector, has got the unique<br/><br>
quality to let the suns short wave ultraviolet radiation through and to close in the long wave<br/><br>
infrared radiation.<br/><br>
The solar window can be controlled automatically, through a light sensor, or manually.<br/><br>
The manual control is important in case they are installed in houses but the automatic control<br/><br>
is preferable because it optimizes the solar energy exchange.<br/><br>
The heat insulated abilities increased radically when the reflectors were closed.<br/><br>
The U-value decreased from 2,4 W/m²K, with open reflectors, to 1,3 W/m²K, with closed<br/><br>
reflectors. We hoped to reach the U-value of an insulated wall with an approximated U-value<br/><br>
of 0,5 W/m²K, this of course depending on the insulation and thickness of the wall.<br/><br>
6<br/><br>
The heat insulating parts of the solar window are the double glass and the five reflectors<br/><br>
insulated with four centimetres of polystyrene. Thicker insulation in the reflectors was not<br/><br>
interesting because then the aesthetic look was not pleasant. This, however, might be<br/><br>
interesting if the solar windows are installed in other places than houses, which was the<br/><br>
purpose from the beginning. One way to increase the heat insulating abilities of the solar<br/><br>
window is to install a double glass with better insulation as long as the sunlight transmission<br/><br>
does not decrease. These double glasses are probably much more expensive. The possibilities<br/><br>
to decrease the U-value by insulating the solar window in other ways are fairly low because of<br/><br>
the movable parts in the construction.<br/><br>
A solar window can yearly contribute 360 kWh/m² of solar energy, including both active and<br/><br>
passive solar energy, and will approximately cost SEK 2500 per m² with industrial<br/><br>
production. The solar energy will cost SEK 0.69 per kWh calculated to be paid over a ten year<br/><br>
period. The life time of the solar window is longer than ten years, probably up to thirty years.<br/><br>
The running costs that are normally approximated to 10 % of the investment cost will be<br/><br>
added.<br/><br>
A normal two glass window heading south yearly transmits 609 kWh/m² and the sun window<br/><br>
yearly transmits 368 kWh/m² given that the reflectors are closed to work as sun shields when<br/><br>
the sun radiation exceeds 300 W/m². This means that the solar window decreases the sun light<br/><br>
in pouring by yearly shading away 241 kWh/m² in comparison with a two glass window.<br/><br>
The simulation in Minsun was used to approximate the active solar energy supply for every<br/><br>
hour over a year for Stockholm city. The simulation shows that the sun window yearly<br/><br>
contributes with 234 kWh/m² active solar energy, where 79 kWh/m² is sun electricity and 155<br/><br>
kWh/m² is sun heat. In the real case approximately 180 kWh/m2 active solar energy will be<br/><br>
contributed, where 60 kWh/m2 is solar electricity and 120 kWh/m2 is sun heat.<br/><br>
Simulation in ParaSol was used to approximate the passive sun heat contributed through open<br/><br>
reflectors and losses through closed reflectors. The total passive sun heat contribution is<br/><br>
yearly approximated to 210 kWh/m². Where approximately 180 kWh/m2 yearly contributes to<br/><br>
the house in the real case.<br/><br>
18 m2 solar windows at Solgården in Älvkarleby approximately give 6500 kWh/year, which<br/><br>
gives 26 % coverage of the total energy need at Solgården. Provided that the total energy need<br/><br>
is 25000 kWh/year. At Solgården the remaining heat will come from an already installed<br/><br>
pellet pan and because the solar cells do not cover the electricity need electricity will also be<br/><br>
installed.<br/><br>
Enlargement of the solar window area will in this case not be meaningful because the solar<br/><br>
windows give 100 % coverage during the summer months which the dimension is based on.<br/><br>
Enlargement of the solar window area means that you risk to get a lot of surplus heat during<br/><br>
the summertime and only a small enlargement of the total heat need coverage.},
author = {Johansson, Tobias},
isbn = {91-85147-09-5},
language = {swe},
pages = {48},
publisher = {ARRAY(0xb92cc98)},
series = {EBD-R--05/8},
title = {Utvärdering av solfönster, en integration av solhybrider och solskydd},
year = {2005},
}